1. Field of the Invention
The present invention relates to a method of manufacturing a vertical nitride light emitting device, and more particularly, to a method of manufacturing a vertical nitride light emitting device which can reduce damage to crystals due to thermal impact during a laser lift-off process, thereby improving a yield.
2. Description of the Related Art
In general, single crystals constituting a group III nitride light emitting device are formed on particular types of growth substrates such as sapphire substrates and silicon carbide SiC substrates. However, the sapphire substrate is an insulation substrate, which greatly limits the arrangement of electrodes in a nitride light emitting device. In a conventional nitride light emitting device, since both electrodes are disposed horizontally, the current flows horizontally along a narrow path. Due to such narrow current flow, the light emitting device has increased forward voltage Vf, thus having degraded current efficiency and weak electrostatic discharge effects. In addition, the insulation substrates such as the sapphire substrates have relatively low heat conductivity, thus having ineffective heat discharge characteristics.
To overcome such a problem, a nitride light emitting device having a vertical structure is required. However, the nitride light emitting device having a vertical structure entails a process of removing the sapphire substrate in order to form contact layers on upper and lower surfaces thereof.
As shown in FIG. 1, the sapphire substrate 21 is removed via a laser lift-off process after a conductive substrate 31 is attached onto a light emission structure 25 composed of nitride single crystals. However, the sapphire 21 has a thermal expansion coefficient of about 7.5×10−6/K, whereas GaN single crystals constituting the light emission structure 25 has a thermal expansion coefficient of about 5.9×10−6/K and a lattice mismatch of about 16%. In addition, even if a GaN/AlN buffer layer is formed, a lattice mismatch of several % remains. Thus, even if the nitride light emission structure 25′ is separated into individual units, the heat generated during irradiation of laser beam onto the sapphire substrate 21 is transferred laterally along the sapphire substrate 21, causing thermal stress, thereby damaging the nitride crystals.
In addition, when the sapphire substrate or wafer is removed from the nitride single crystals after irradiating the laser beam, it is highly likely that there may be collisions between the sapphire substrate being detached and a portion of the nitride single crystals, consequently resulting in a low yield.